The rotation of powered driver shafts is commonly applied to rotary driven shafts, or to linear mechanisms to change their position, either rotationally or linearly. In many of these applications, continuous application of power to produce a steady continuous output is desired. In others, an incremental stepping operation is preferred, and for all these applications a considerable number of drives have been devised. Ratchet movements and stepper motors are two well-known examples.
Designers of incremental drives have over the years responded to new requirements imposed in their respective arts. In most cases these responded to needs which, as to those known to the applicant herein, nicely fitted the situations in which they were to function. Examples of such efforts are shown in U.S. patents to Hockett 430,021, Hundhausen 646,287, and Harbidge 3,363,673. Of less pertinence, but perhaps of greater interest is Knollin 461,441.
It is of at least historical interest to observe that the prior art efforts were generally directed toward heavy duty applications which were of commercial interest at their time. The propulsion of conveyances, the driving of rotary kilns, or the positioning of machine tool tables were, and for decades remained, primary contemporary requirements of heavy American industry.
However, these applications were succeeded by requirements which formed part of a more sophisticated and lighter emerging technology. Smaller, finer movements for lighter devices became of importance which the older devices could not supply. Modern examp1es of new applications are to be found in robotics, where the equivalent is needed of a scissors movement--the clamping action of a finger versus an opposable thumb, the twisting movement exemplified by rotation of the wrist, or a small linear displacement. It is not surprising that the prior art heavy duty devices did not provide the needs of the next generation, even though both had the same objective of incremental power transmission and high ratio power reduction. Convenience, least weight, and transmission of relatively low power loads were of little or no interest then. If a mechanism weighed an extra few pounds it did not matter. Today it does.